In third-generation CT, raw data is collected by rotating a rotating ring equipped with one or more sets of X-ray tubes and X-ray detectors. The rotating ring has reached the highest rotational speed of 0.275 s/rot. In physics, the centrifugal force generated by rotation is proportional to the square of angular velocity. For this reason, it is difficult to greatly increase the current rotational speed of the rotating ring. In fifth-generation CT, an electron gun is used to emit an electron beam from the rear side of a gantry, and the electron path is deflected by using a coil to cause the electron beam to strike anodes arrayed on a circumference, thereby generating X-rays. An electron beam is deflected onto the circumference to implement CT. In fifth-generation CT, since X-ray detectors are arrayed on a circumference, the scan time is determined by the electron beam scan time. The scan time according to the fifth-generation CT has reached 50 ms to 100 ms.
U.S. Pat. No. 7,634,045 has proposed a scheme of rotating only the detector side collimator (post-collimator) mounted on a gantry in fifth-generation CT. U.S. Pat. No. 7,634,045 has also presented fifth-generation CT which can also cope with spectral CT by changing an applied voltage for each place. This scheme, however, uses an electron gun, and hence the overall size of the system becomes large. In addition, since an X-ray detector and an electron beam are offset from each other in terms of a positional relationship, this scheme is not suitable for three-dimensional scanning (volume scanning).